Blade for use in a fluid flow machine



BLADE FOR USE IN A FLUID FLOW MACHINE Filed Nov. 14, 1968 2 Sheets-Sheet1 FIG] .[zvnw ToRS I u: K Pay/M0010 3/120 7200MB fiE/Vc MR 0 QRMNTQMAMM, 4 M GMAW Arr n AIL- v5 Dec.22, 1970 ,R,B. ETAL 3,549,273 1 BLADEFOR USE IN A FLUID FLOW MACHINE Filed Nov. [14, 1968 v z Sheets-Sheet zI LKENTORS Jicx FAyMo/vp (BIRD Poo/v5) 7R EN6H/IRD BRyANT I Arro'ausysUnited States Patent 3,549,273 BLADE FOR USE IN A FLUID FLOW MACHINEJack Raymond Bird, Chellaston, and Rodney Trenchard Bryant, Balsham,Cambridge, England, assignors to Imperial Metal Industries (Kynoch)Limited, Birmingham, England, and Rolls-Royce Limited, Derby, England,both British companies Filed Nov. 14, 1968, Ser. No. 775,773 Claimspriority, application Great Britain, Nov. 16, 1967,

52,261/67 Int. Cl. Fold 5728 US. Cl. 416241 2 Claims ABSTRACT OF THEDISCLOSURE A gas turbine engine blade has its root and blade portionsrespectively made of difierent alloys having the same base metal such asniobium or titanium.

This invention concerns a blade for use in a fluid flow machine such,for example, as a gas turbine engine. Thus, although the invention isnot so restricted, the blade may be a. turbine rotor blade although theinvention is also applicable to compressor blades. The term blade is,moreover, used in a wide sense as including nozzle guide vanes.

A turbine rotor blade is usually composed of two principal parts, namelya blade portion, against which the impelling gases impinge, and a rootportion which anchors the blade to a support and transmits forces fromthe blade to the support.

Blades for gas turbine engines are usually produced by forging andmachining suitable alloy material. The choice of alloy for the blade hasbeen a compromise to meet the operating conditions expected for both theroot and blade portions, this compromise having regard, for example, tothe nature of the impinging gases and to the operating temperatures andstresses.

For example, the blade portion must be strong and must be subject toonly a limited amount of creep deformation under high centrifugalstresses at elevated temperatures, and the blade portion, even whensuitably coated, must be resistant to oxidation by the gases employed.

The root portion, on the other hand, requires relatively high strengthto withstand the high centrifugal bending and vibrational stressesimposed during operation, but is not subject to such high temperatures.The root portion, moreover, should also be oxidation-resistant so as towithstand the lower temperatures without it being necessary to provideit with an oxidation-resistant coatmg.

According, therefore, to the present invention, there is provided ablade for use in a fluid flow machine in which at least part of the rootand blade portions of the blade are respectively made of differentalloys.

The root portion and/or the blade portion may be made up of a number ofparts which are respectively made of different alloys.

Preferably the immediately adjacent parts of the root and blade portionsare respectively made of different alloys.

Each of the alloys may be based upon a common metal. Thus each of thealloys may, for example, be a niobium based or a titanium based alloy.

The different parts of the blade are friction welded to each other.

The invention also comprises a method of making the said bladecomprising welding together the root and blade portions of the blade, atleast the adjacent parts of the root and blade portions beingrespectively made 3,549,273 Patented Dec. 22, 1970 of ditferent alloyshaving coetficients of expansion such as to prevent the blade fromfracturing at the weld.

'The invention additionally comprises a method of making the said bladecomprising forming a weld between a root blank and a blade blank, andforging the blade with the said weld disposed substantially at thejunction between the root and blade portions of the blade, at least theadjacent parts of the root and blade blanks being respectively made ofdifferent alloys having coeflicients of expansion such as to prevent theblade from fracturing at the weld.

The invention is illustrated, merely by way of example, in theaccompanying drawings, in which:

FIG. 1 is a diagrammatic view, partly in section, of a gas turbineengine provided with blades in accordance with the present invention,

FIG. 2 is a perspective view of one of the blades of the engine of FIG.1,

FIG. 3 is a broken-away sectional view of two united blanks which may beused in the formation of a blade,

FIG. 4 is a diagrammatic view of the united blanks after they have beenforged to produce a flattened cross section, and

FIG. 5 illustrates the position of a fracture in a tensile test pieceformed from the united blank of FIG. 4.

In FIG. 1 there is shown a gas turbine engine 10 having in flow series acompressor 11, combustion equipment 12, and a turbine 13, the turbineexhaust gases being directed to atmosphere through an exhaust duct 14.

The turbine 13 is provided with a rotor 15 which carries rotor blades16.

As shown in FIG. 2, each of the rotor blades 16 comprises a fir treeroot portion 20 and a separate blade portion 21 which has been welded tothe root portion 20 at a weld 22. The root portion 20 and blade portion21 are respectively made of different alloys which have coefiicients ofexpansion such as to prevent the blade 16 from fracturing at the weld22.

Each of the said alloys is preferably based upon a common metal, such asniobium. Thus the blade portion 20 may be made from a niobium basedalloy containing 17% tungsten, 3.5% hafnium and 0.08% carbon (all thesepercentages being by weight), while the root portion 21 may be made ofniobium based alloy containing 10% molybdenum and 10% titanium (allthese percentages also being by weight).

If desired, only the immediately adjacent parts of the root and bladeportions may be respectively made of the said different alloys, althoughpreferably the whole of the root and blade portions are respectivelymade of the said different alloys.

Alternatively, both the root portion 20 and the blade portion 21 may, ifdesired, be made up of a number of parts which have been respectivelymade of different alloys.

As illustrated diagrammatically in FIG. 3, each of the blades 16 may bemade by forming a weld 22, e.g., a friction weld, between a root blank23 and a blade blank 24 and forging the blade so that the finished bladehas the weld 22 disposed substantially at the junction between the rootportion 20 and blade portion 21 of the blade.

In order to effect the said friction weld, the blanks 23, 24 are placedcoaxially in end-to-end relationship and one of them is held stationarywhile the other is rotated at high speed while forcing adjacent ends ofthe blanks together. When a sufliciently high temperature has beengenerated, rotation of the rotating blank is stopped and the adjacentends are forced together (e.g., under a load of 1.5 tons for blanks 23,24 having a diameter of to produce the weld 22. This also causes theformation of flash 25 from the softer alloy of the blank 24, and

there may also be some flash (not shown) from the harder alloy. Thisflash is then removed and the united blank so produced is then forged toproduce the final blade.

FIGS. 4 and 5 illustrate test pieces formed from the united blank. Thusin FIG. 4 the united blank, after having been heated and maintained at.1300 C. in vacuum for one hour, was subsequently forged at 800 C. inair to produce the flattened cross section shown in FIG. 4. Examinationof this united blank showed that the weld 22 was sound.

Moreover, as shown in FIG. 5, a standard tensile test bar 26 wasmachined from the united blank. A tensile test at 450 C. producedfailure at a stress of 29.3 tons per square inch at a point away fromthe weld 22, indicating that the weld 22 was stronger than the weaker ofthe parent alloys.

A turbine blade forged and machined from the united blank referred toabove should not require special heat treatment nor the provision of acoating for its root portion. This is because of the strength andoxidation resistance which the root portion possesses below 600 C.,while the blade portion has good stress rupture strength at bladeoperating temperatures.

We claim:

1. A blade for use in a gas turbine engine, the blade being subjected toelevated temperatures and capable of withstanding high stresses when inuse and comprising: a root portion and a blade portion united by afriction weld therebetween, said root portion and said blade por- 4 tionbeing made of different alloys, each of which is a niobium based alloyor a titanium based alloy, and the alloy of said base portion having acoeflicient of expansion compatible with the alloy of said blade portionwhereby fracture of the friction weld is prevented.

2. A method of making a blade for use in a gas turbine engine atelevated temperatures and capable of withstanding high stresses, theblade having a root portion united to a blade portion by a weld whichresists fracture, the steps comprising: forming a root blank of aniobium or titanium based alloy having a predeterminedacoefiicient ofexpansion, forming a blade blank of a dilferent niobium or titaniumbased alloy, but having a compatible coeflicient of expansion, frictionwelding the root blank to the blade blank to form the weld therebetween,and then forging the blade portion from the blade blank and forming aroot portion from the root blank so as to dispose the friction weldtherebetween.

References Cited UNITED STATES PATENTS 1,948,793 2/1934 Lewis 25377(M)UX2,019,329 10/1935 Warren 29--156.8

2,807,435 9/1957 Howlett et a1. 25377(M) FOREIGN PATENTS 535,229 4/1941Great Britain 159(M) 696,715 9/ 1953 Great Britain 416-223 EVERETTE A.POWELL, JR., Primary Examiner

